1. Field of the Invention
This invention relates to a transfer switch for differential type actuators which supplies pressure to and controls a plurality of differential type actuators capable of operating in response to a pressure difference appearing on opposite sides of a piston or diaphragm.
2. Description of the Prior Art
To achieve some linear binary mechanical control the differential type actuator is used. For example, a 2WD/4WD changeover system for the automobile transfer section uses such actuators. The foregoing changeover system is designed so that the vacuum pressure of a manifold is made to act on respective chambers of the differential type actuator via solenoid valves. Its control is of the electric type in which when the differential type actuator is to be actuated in one direction, a solenoid valve connected with a chamber positioned in the working direction of the actuator is energized to suck the air within the chamber and the opposite chamber is opened so as to be supplied with the atmosphere. When the actuator is to be actuated in the opposite direction to the above, suction and supply of the air are reversed.
Regarding the mechanical transfer switch, U.S. Pat. No. 4,328,832 discloses a multistage changeover type orifice device. This multistage changeover type orifice device has a plurality of orifice passes provided in one input route and can change over the degree of throttling of fluid in multiple stages by controlling opening/closing of these orifice passes by means of control members. In case the foregoing device is used to control a plurality of differential type actuators, its individual output ports are connected with the chambers on one side of the differential type actuators, with those on the other side being opened.
In case the solenoid valve is used as the transfer switch for control of the differential type actuator, two solenoid valves are needed per differential type actuator to control individual chambers. Accordingly, such configuration is not advantageous from the point of view of costs, arrangement space, weight, etc. in case a plurality of differential type actuators are to be controlled at a time.
The mechanical multistage changeover type orifice device cannot make good use of the function of the differential type actuator because it has only one input route, and thus is not suited for control of such actuators.